The invention relates in general to the field of electro-optical and optoelectronic devices. More specifically, the invention relates to electro-optical devices comprising a stack of III-V semiconductor gain materials, optoelectronic devices comprising such electro-optical devices and methods of fabrication thereof.
For the successful monolithic integration of III-V optoelectronic devices (e.g. lasers, detectors, semiconductor optical amplifiers, or SOAs) on silicon (Si) Complementary Metal Oxide Semiconductor (CMOS) platforms, shallow III-V stacks are necessary (typically less than 500 nm thick). The mode used in such structures is typically a hybrid mode, meaning it is partially located in the III-V stack and partially in the lower silicon waveguide core. For an efficient transfer of the mode between the III-V stack and Si, structures are sought which enable an adiabatic coupling. However, to avoid a tapering (i.e., a gradual change of width) of the III-V stack, which would lead to the occurrence of unpumped regions and eventually to optical losses, only the Si waveguide core is tapered. This allows for high output powers (in case of SOAs and lasers) and low losses during the mode transfer.
For example, FIG. 1 illustrates a typical (prior art) configuration, wherein a Si substrate layer 100 is covered by a buried oxide 101. A waveguide core 102 is structured from the top Si layer. The waveguide core 102 is cladded by a SiO2 layer 103. A III-V gain stack 105 is brought into contact with the cladded structure 100-103 via a bonding layer 104. The III-V stack is then cladded with a second SiO2 layer 106. Mode transfer is achieved via a tapered Si waveguide core. However, for a large gap (large thickness of cladding 103), e.g., for a gap of 600 nm and a III-V stack height of 250 nm, a mode with a wavelength in a range as typically used in telecom applications cannot be transferred from Si to III-V and vice versa.